Hi All, there was a PBS special, they talked about Wash DC, Congress was about ready to break up GM, they decided to ask American Motors to build a city buss for DC, but they couldn't come up with engines that didn't break down frequently, it was the predessor of american general when they added gm power trains, I have a CNG, compressed natural gas dedicated, F250 (meaning it only uses CNG, not a bifuel), GGE, Gas Gallon Equivalent, is roughly the same, nat gas to gasoline, roughly the same time to fill up, faster at 3600psi than 3000psi, mine is a great truck if it wasn't for the Ford 5.4 ltr engine that spits out spark plugs, lvmci...

Clifford, you said, "Pilot/FJ are spending tons of cash betting on it 100+ of their truck stops are supposed to have natural gas refilling stations by years end + another 100 by the end of 2014"!Pilot/Flying J seems to be in a heap 'O' trouble with the feds, their offices were raided April 15th by the FBI and IRS. Supposedly they were not paying rebates like they were supposed to. I suspect the real reason is that they have probably run afoul of the anti-trust provisions of the Pilot and Flying J merger. Just my guess!Jack

You have to also remember the massive manufacturing capability that GM had for decades. With the hound and Trailways ordering hundreds of buses, General Motors Diesel Div., (later Detroit Diesel div.) had the capacity to produce the engines above all others.

Could it be that the 2 cycle D.D. was invented for WWII tanks. I read that it was designed so that you could get maximum power in the smallest possible space and use less the flameable diesel, instead of gasoline. Then after the war, there was a surplus of these engines and all of the manufacturing capability was there. So, the market at the time was long haul buses, such as Greyhound.

I do not know if the Detroit 671 was specifically designed for WW2 Tanks or not, (too small) but it did seem to power just about everything a horrible World War needed in stuff that needed to be powered....all the way from dinky hand held pavement polisher/smoothers, (still big) all the way to twin quad, (later quad quad?) 671 DDs powering a very large, very slow ocean going LST (landing ship..tank)

Cummins had a pancake 743 and earlier smaller models that was used in lots of the smaller, less known coach manufactures like Crown Supercoach, Mack, White, Gillig and others. The mill was just laided 70-80 degress on its left side. Very flat, thus the nickname "pancake motor". My old Crown Supercoach had one.

White had a flat 12. Hall Scott and International also had many "flat" gas engines designed to fit under a bus floor. Years ago I got to drive all three with the Kern High School District in CA starting in the year 1969 or sooss. Rumour had it DD designed their pancake mill for a large school district to use in their Crown fleet instead of using the excellent pancake Cummins.

Actually, I think DD had a pancake version before the CA school bus rumour, as well as weird applications like the engine upside down, up on one end, or with clutches on both ends. Our Fire apparatus had two starters on the DDs for some unknown reason.

Seems lots of different mills were tried in coaches. DD was probably the major player because, like Cummins, they had all that huge WW2 manufacturing capacity left over from WW2...and that the DD was, (is still?) a very compact adaptable design still working worldwide. DDs are soooss cool. HB of CJ (old coot) Sorry abouts speeeling

Cummins makes a pancake engine based on their KTA block (1150cu/in) and putting out 750hp. Made for self powered railroad passenger cars-typically two to each.

Yes Cummins makes a dual fuel ISX15 that actually works quite well. But-in California, CARB (California Air Resource Board) doesn't recognize the dual fuel engine as a true natural gas engine since it can run on 100% Diesel if it runs out of natural gas. Dual fuel engines have been around for many years. Sewage pumping plants used them using the methane from the waste to run the engines (90% methane 10% Diesel to fire it). Good Luck, TomC

We don't thread drift at all here...ever. So anyone know how to fix my headlight? It's burnt out. Ok, no really, I must say, as we travel and tour, we meet a lot of older gents who fondly recall the "screamin jimmys". Just talked to one this past weekend. Something about the simplicity of these two strokes, the abuse they'll take, and the way they sound evokes some pretty soft feelings from a lot of guys. I love our bus, but I do also know that better, more efficient, and in some cases more reliable powerplants are available today and I hope someday to be in a 4 stroke.

The thing is, if Detroit up graded the 2 strokes to modern day electronic common rail fuel injection (the engines would loose that wonderful compression sound), the 2 strokes could be viable. Modifying a 4 stroke is just a lot easier. Plus the fuel mileage is just plainly better with a 4 stroke. Mileage estimates are as follows:Using a mechanical 2 stroke as the basis:-Upgrade to either a DDEC 2 stroke or a mechanical 4 stroke will get about 1 more mpg.-Upgrade to an early electronic 4 stroke get another 1 mpg more.-Upgrade to a 2010 or newer 4 stroke engine using DEF, get another 1mpg more.So a bus getting 6mpg with a mechanical Detroit could get up to 9 or 10 mpg with a new designed 4 stroke. Good Luck, TomC

Something is wrong here TomC the Prevost with the DDEC 8v92 with a 755 transmissions got around 5 and 6 mpg the newer ones with the 14L smog engines get 5 and 6 mpg with the 6 speed World transmission they were around 7 + before the EGR engines I love the Prevost guys they tell it like it is

Hemphill tells me the way the entertainers buses are pushed at 75mph they are are 5 mpg tops with series 60 or the D13 Volvo engine

I talked with Don Fairchild about this once and threw off the comment that four strokes get better fuel mileage. He was quick to correct me and said that a two stroke could do as well or better, pound for pound and hp for hp. I think the reason so many buses came with the DD series two stroke is they made good power for the weight, they were economical to buy and run, they were very reliable, they could be rebuilt easily and quickly be back in service. Exactly the same reasons anyone would spec out and buy an engine today. They were in all the buses because they were the best choice for the time.

You have to remember that when GM built buses, they never offered CUMMINS or others and why should they, they owned DETROIT DIESEL at the time and until the 1970's(I think) they were just GM not DETROIT. So when operators bought buses built by GM's competitors, they wanted the same engines especially if they had GM buses and they wouldn't have to get used to a new engine. But as others said, they were good. Even when GM was long out of the bus building business, DETROIT had most of the market in part because CUMMINS didn't have a good bus engine yet. But that all began to change in the 1980's when CUMMINS started becoming available in transit buses and over the road buses in the 1990's and surpassed the grand old DETROIT 71 and 92 engines. The final nail in the coffin came when DETROIT rolled out the SERIES 60 & 50 engines so one could see that when even DETROIT would move away from the 2 cycle, you know the end was coming. They came out with an 8.2L V8 for GM and FORD trucks and various school bus builders in 1980 that was 4 cycle so even then they were moving away from 2 stroke. The EPA was a factor as well. But since most diesels were 4 cycle anyway, DETROIT figured just join them.

Hard to believe how fast time goes. At least around here, there are virtually no buses in service with the old 71 or 92 engines so no unique sound. There are a few fire apparatus in the area from the 1990's that still have those. Some of them you can hear over the siren. Now with this new clean technology, they are almost quieter than the family sedan.

As to mileage differences-I'm talking about fuel mileage for our useage. Not commercial buses that sit and fast idle for sometimes hours at a time.

Yes Don Fairchilds off road engines come up to Tier 2-which is like a 2002 certification. Don would need to go with a Diesel Particulate Filter to get up to 2007 standards. And for 2010 to go with DEF with no more then .02grms for nitrous Oxides. International was at .05, which is clean, but was still 2.5 times more dirty then the new engines. Don has entertained Bendix, Bosch and others to work with him to create a common rail fuel injection system-but no one wants to do it. Good Luck, TomC